Add asset pipeline and professionalize theme

Introduce a Node build system for minified CSS/JS with content hashes,
add PWA support, i18n helpers, accessibility improvements, and more
translatable strings. Move theme configuration from bookmarks to
localStorage, add Playwright tests, and set up CI workflows.

shaarli-pro/server.requirements.html

@@ -20,7 +20,7 @@
 
         <div class="col-md-10 col-md-offset-1">
             <div class="card">
-                <div class="card-header">PHP</div>
+                <div class="card-header">{'PHP'|t}</div>
                 <div class="card-body">
                     <p style="margin-bottom: 1.5rem;">
                         <strong>{'Running PHP'|t} {$php_version}</strong>